How do a "test" a new lens for abnormalties?

dehanson1 · 01-11-2010, 05:05 PM

Ive been seiing a lot of post about people buying new sigma lenses that were "soft" or "out of focus" at certain points ect. I am new to this and thinking about buying a sigma lense. How can a newbie like me "test" a lens when it arrives to see if its funcctioning properly?

asdf · 01-11-2010, 05:16 PM

Originally posted by dehanson1

Ive been seiing a lot of post about people buying new sigma lenses that were "soft" or "out of focus" at certain points ect. I am new to this and thinking about buying a sigma lense. How can a newbie like me "test" a lens when it arrives to see if its funcctioning properly?

Put your camera on a stable tripod and use the mirror lockup feature and preferably a shutter release cable. Turn off SR. Shoot under fluorescent light. Find a flat target, parallel to the sensor.

erickallemeyn · 01-11-2010, 05:20 PM

1. grab a newspaper, lay it flat on a table

2. Set your camera's autofocus to the center point only. Turn the dial to Av mode and set the Aperture to the lowest number possible and zoom all the way in. You should probably use a tripod.

3. point the camera at a 45* angle to the newspaper

4. autofocus on a specific word in the newspaper - remember what word it was!

5. Now, do it again, but manually focusing the lens on the same spot.

6. Upload both shots to the computer to test

-Make sure the text you focused on in the first shot is the *most* in focus word. Words above and below it should be slightly out of focus.

-Compare 'sharpness' of the text that's in focus for both shots. Don't freak if the manually focused one is slightly sharper, it usually is

Wheatfield · 01-11-2010, 05:34 PM

I just go out and take pictures.
I always find something to take a picture of that tests my camera's mettle.

**Lowell Goudge** · 01-11-2010, 05:36 PM

I only do one real "test" before I go out and shoot

I check exposure at all F stops by shooting a block wall or paved roadway and then checking the average grey scale value. with neutral contrast, it shoudl be centered at about 110-120 and each F stop within a +/- 1.5 stop band has a range of about 45 greyscale around the 110-120 value

Then I go out and shoot. If I have issues with sharpness afterwards I might try focus tests but these are so badly designed they can be misleading. the best focus test is to focus on a flat wall at right angles and then blow this up for the detail, if it is sharp you don't have a focus issue

asdf · 01-11-2010, 05:56 PM

Originally posted by Wheatfield

I just go out and take pictures.
I always find something to take a picture of that tests my camera's mettle.

Hmm...

http://www.youtube.com/watch?v=0toBw68L5Y4

jimH · 01-11-2010, 05:58 PM

subscribe to this thread

440roadrunner · 01-11-2010, 06:45 PM

Originally posted by asdf

.............Shoot under fluorescent light................

I do not understand why you would recommend this

asdf · 01-11-2010, 06:49 PM

Originally posted by 440roadrunner

I do not understand why you would recommend this

Under tungsten light, *some* cameras consistently front focus with every lens.

Wheatfield · 01-11-2010, 07:08 PM

Originally posted by asdf

Hmm...

http://www.youtube.com/watch?v=0toBw68L5Y4

HAR!!!!!!!!!
I went through that with the Zone System.
I could never get Tri-X to give me a perfect curve.
I hated Tri-X from the moment I bought a densitometer.

01-11-2010, 05:05 PM	#1
dehanson1 Junior Member Join Date: Nov 2009 Location: mississippi Posts: 38	How do a "test" a new lens for abnormalties? Ive been seiing a lot of post about people buying new sigma lenses that were "soft" or "out of focus" at certain points ect. I am new to this and thinking about buying a sigma lense. How can a newbie like me "test" a lens when it arrives to see if its funcctioning properly?

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01-11-2010, 05:16 PM	#2
asdf Veteran Member Join Date: Jan 2009 Location: Canada Posts: 1,252	Originally posted by dehanson1 Ive been seiing a lot of post about people buying new sigma lenses that were "soft" or "out of focus" at certain points ect. I am new to this and thinking about buying a sigma lense. How can a newbie like me "test" a lens when it arrives to see if its funcctioning properly? Put your camera on a stable tripod and use the mirror lockup feature and preferably a shutter release cable. Turn off SR. Shoot under fluorescent light. Find a flat target, parallel to the sensor.

01-11-2010, 05:20 PM	#3
erickallemeyn Senior Member Join Date: Dec 2009 Location: United States Posts: 112	1. grab a newspaper, lay it flat on a table 2. Set your camera's autofocus to the center point only. Turn the dial to Av mode and set the Aperture to the lowest number possible and zoom all the way in. You should probably use a tripod. 3. point the camera at a 45* angle to the newspaper 4. autofocus on a specific word in the newspaper - remember what word it was! 5. Now, do it again, but manually focusing the lens on the same spot. 6. Upload both shots to the computer to test -Make sure the text you focused on in the first shot is the most in focus word. Words above and below it should be slightly out of focus. -Compare 'sharpness' of the text that's in focus for both shots. Don't freak if the manually focused one is slightly sharper, it usually is

01-11-2010, 05:34 PM	#4
Wheatfield Moderator Join Date: Apr 2008 Location: The wheatfields of Canada Posts: 15,991	I just go out and take pictures. I always find something to take a picture of that tests my camera's mettle.

01-11-2010, 05:36 PM	#5
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,892	I only do one real "test" before I go out and shoot I check exposure at all F stops by shooting a block wall or paved roadway and then checking the average grey scale value. with neutral contrast, it shoudl be centered at about 110-120 and each F stop within a +/- 1.5 stop band has a range of about 45 greyscale around the 110-120 value Then I go out and shoot. If I have issues with sharpness afterwards I might try focus tests but these are so badly designed they can be misleading. the best focus test is to focus on a flat wall at right angles and then blow this up for the detail, if it is sharp you don't have a focus issue

01-11-2010, 05:56 PM	#6
asdf Veteran Member Join Date: Jan 2009 Location: Canada Posts: 1,252	Originally posted by Wheatfield I just go out and take pictures. I always find something to take a picture of that tests my camera's mettle. Hmm... http://www.youtube.com/watch?v=0toBw68L5Y4

01-11-2010, 05:58 PM	#7
jimH Veteran Member Join Date: Apr 2009 Location: South Central Nebraska - USA Photos: Gallery \| Albums Posts: 1,771	subscribe to this thread

01-11-2010, 06:45 PM	#8
440roadrunner Inactive Account Join Date: Nov 2009 Posts: 14	Originally posted by asdf .............Shoot under fluorescent light................ I do not understand why you would recommend this

01-11-2010, 06:49 PM	#9
asdf Veteran Member Join Date: Jan 2009 Location: Canada Posts: 1,252	Originally posted by 440roadrunner I do not understand why you would recommend this Under tungsten light, some cameras consistently front focus with every lens.

01-11-2010, 07:08 PM	#10
Wheatfield Moderator Join Date: Apr 2008 Location: The wheatfields of Canada Posts: 15,991	Originally posted by asdf Hmm... http://www.youtube.com/watch?v=0toBw68L5Y4 HAR!!!!!!!!! I went through that with the Zone System. I could never get Tri-X to give me a perfect curve. I hated Tri-X from the moment I bought a densitometer.